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From: Lance Yang In-Reply-To: <20260430070217.39679-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ik61ozafzue65gd8oawu3fce4ei34rrm X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9179E4000A X-Rspam-User: X-HE-Tag: 1777533179-41278 X-HE-Meta: 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 C/BY4cuy +Rbu5BuqLMVqlZQXiH8qLuHUXM/EDO3GSCeonYXjpRHsEyZnIZv6MCLomzOblhyfgLuJ/HkjdK7J1ZNV6KEAOFSZB3dBepAsJccxc3AhEc9VvSPWA7xKHRYLE/zJs+XMO66DSKzKMbnLVTTFb8STMOainNdAlSjWGD+zoUgUlV1XexmjhSCmigRH1VcNa7Rb0ezy4OlW0HZ2MWCZZWdM2V2Rbd2V/LkNYOBEZtz5lBTX6Qy1boOzq4KVshk/4JS+UxRPgZ4G61aaFPTALQQRTz9SomtUYImsXT/3j1e4C1HuJlBwx01S775E49aicWZMkbvjamnH0P4eERwk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/4/30 15:02, Lance Yang wrote: > > On Thu, Apr 30, 2026 at 02:34:20PM +0800, Bibo Mao wrote: >> >> >> On 2026/4/30 下午12:28, Lance Yang wrote: >>> >>> On Thu, Apr 30, 2026 at 12:11:20PM +0800, Bibo Mao wrote: >>>> when executing command "make check" with qemu software, there is >>>> error report like this: >>>> BUG: Bad rss-counter state mm:00000000972846bc type:MM_FILEPAGES val:-4096 Comm:bios-tables-tes Pid:27802 >>>> BUG: Bad rss-counter state mm:00000000752180c5 type:MM_FILEPAGES val:-2048 Comm:worker Pid:27815 >>>> BUG: Bad rss-counter state mm:000000009c2f6a61 type:MM_FILEPAGES val:-2048 Comm:qom-test Pid:27825 >>> >>> Good catch! >>> >>>> The problem is that when application exits, rss counter is calculated >>>> with huge_zero_pmd huge page, instead it should be skipped. >>> >>> Looks like the same problem[1] we discussed recently. >>> >>> [1] https://lore.kernel.org/linux-mm/74a75b59-2e13-3985-ee99-d5521f39df2a@google.com/ >>> >>>> Signed-off-by: Bibo Mao >>>> --- >>>> mm/huge_memory.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>> index 970e077019b7..3cbea344d4a2 100644 >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -2423,6 +2423,9 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma, >>>> { >>>> const bool is_device_private = folio_is_device_private(folio); >>>> >>>> + if (is_huge_zero_pmd(pmdval)) >>>> + return; >>>> + >>> >>> The huge zero PMD should not be returned by vm_normal_page_pmd() or >>> vm_normal_folio_pmd() as a normal folio. If it reaches >>> zap_huge_pmd_folio(), we already made the wrong normal-vs-special >>> decision ... >>> >>> So I don't think we should special-case it in zap_huge_pmd_folio(). That >>> only avoids this RSS decrement :) >>> >>> Could you please check whether the fix[2] also fixes your QEMU test? >>> >>> [2] https://lore.kernel.org/linux-mm/ea1453a6-14c9-4334-ac7e-2758586393b2@kernel.org/ >> yes, I think it will solve this problem. >> >> Only that I think that there should be tlb flush operation after >> pmdp_huge_get_and_clear_full() even with huge_zero_pmd page, so >> tlb_remove_page_size() should be called. Is that right? > > Calling tlb_remove_page_size() is not necessary there :) > > zap_huge_pmd() already marks the PMD range for TLB invalidation right > after clearing the entry: > > orig_pmd = pmdp_huge_get_and_clear_full(...); > tlb_remove_pmd_tlb_entry(tlb, pmd, addr); > > The later tlb_remove_page_size() is guarded by "is_present && folio", > and is for the normal folio case after normal_or_softleaf_folio_pmd() > return one :) Forgot to add: tlb_remove_page_size() queues the folio for freeing via mmu_gather. The shared huge zero folio only needs PMD TLB invalidation, not the delayed freeing :) > > Please correct me if I missed something :D > > Cheers, Lance